1. Field of the Invention
The present invention relates to an electrical property evaluation apparatus for measuring samples, such as samples having a magnetoresistive effect device on a microscale area thereof, and evaluating electrical properties thereof.
2. Description of the Related Art
As everyone knows, there has been generally known a method for gauging a current flowing through a sample and evaluating electrical properties in order to evaluate a sample, such as an electronic material, in electrical properties including the electrical resistance, electrical conductivity, and current-voltage characteristics. For example, as an apparatus for measuring electrical properties of a bulk electronic material, there has been known an electrical property evaluation apparatus, such as an electrical conductivity measuring apparatus having an electrode probe and a spreading resistance measuring apparatus.
Further, as an apparatus for measuring electrical properties including an electrical resistance of a sample of an electronic material, etc. on a micro-scale area of a molecule-size level, there has been known a scanning tunneling microscope. In the scanning tunneling microscope, a conductive metal probe having a tip diameter with a curvature radius of a few tens of nanometers is brought a few nanometers close to a sample to flow a tunnel current between the probe and the sample. Then, the microscope causes the metal probe to scan the sample surface while controlling the distance between the metal probe and sample so as to keep the tunnel current constant, whereby the geometry of the sample surface can be imaged.
Also, there has been known a scanning multi-probe microscope capable of scanning in a magnetic field, which performs the analysis of surface geometry of a material with a vacuum container placed in a strong magnetic field according to a superconducting magnet (see JP-A-2001-50885, Paragraph No. 0002-0011 and FIG. 1, for example). The scanning multi-probe microscope capable of scanning in a magnetic field allows the observation of surface geometry of magnetic materials and semiconductor materials in the condition where a strong magnetic field is applied, e.g. the observation of the change in magnetic domain and the magnetic field-induced phase change process in a magnetic material under a strong magnetic field.
In recent years, various kinds of memory devices, electronic devices, etc. have been developed, and therefore the evaluation of physical properties, functions, characteristics of materials used therefor and electrical properties including the performance of each device has been regarded as important. Especially, it is required to evaluate the characteristics of memories for storing data utilizing magnetism, e.g. MRAM (Magnetoresistive Random Access Memory) with a tunnel magnetoresistive effect device, which is expected to be a next-generation memory device, and RRAM (Resistance RAM) with a large magnetoresistive effect device. This type of device has a small cell area of 0.1 μm2 or less and as such, the need for a technique for locally evaluating electrical properties of such device is increasing to forge ahead with further scaling down in the future.
Evaluation of electrical properties of the magnetoresistive effect device like this and the like, requires controlling the direction of a magnetic field in a magnetic material's layer. In this case, there is generally known a method of using an external permanent magnet, electromagnet, or the like to change the magnetic field in direction and strength and then transferring the sample into a material evaluating apparatus or the like to measure electrical properties of the sample.
Now, in the conventional electrical property evaluation apparatus, such as the above conventional electrical conductivity measuring apparatus having an electrode probe and spreading resistance measuring apparatus, it is possible to macroscopically evaluate a sample because of a large electrode probe tip curvature radius of a few hundreds of micrometers or more, whereas it is difficult to evaluate electrical properties for a micro-scale area of a few micrometers or smaller.
Also in the conventional scanning tunneling microscope, detailed surface information can be obtained by measuring a tunnel current. However, the metal probe thereof cannot be brought into contact with a sample directly because of the gap between the probe and the sample and therefore it is difficult to quantitatively gauge a tunnel current only for the sample.
Further, in the conventional material evaluating apparatus or the like for evaluating electrical properties of magnetoresistive effect devices, etc., the magnetic field in the sample is changed in direction and strength using an external permanent magnet, electromagnet or the like prior to the measurement of the electrical properties, and therefore it is difficult to measure the electrical properties while changing the magnetic field in a micro-scale area on the sample.
In the scanning multi-probe microscope capable of scanning in a magnetic field disclosed in the patent document, JP-A-2001-50885, because a sample is placed under a strong magnetic field produced by a superconducting magnet, there is a disadvantage in evaluating electrical properties of electronic materials and magnetoresistive devices including a tunnel magnetoresistive effect device such that a magnetic field of the magnetic material's layer thereof can be changed in direction, for example, under a weak magnetic field of approximately a few hundreds of gausses.
Moreover, the multi-probe microscope requires a sample set inside the vacuum container and as such, it has difficulties in transferring and operating the sample after once having set the sample. Also, because the size of a sample is restricted in the case of using the vacuum container, there is a disadvantage such that it is unsuitable for wafer-level measurement and evaluation of an electronic material.
The invention was made in consideration of these circumstances. It is an object of the invention to provide an electrical property evaluation apparatus capable of measuring a current, etc. of a sample in a micro-scale area thereof with the sample placed in a space of a magnetic field while controlling the strength of the magnetic field and the amount of change thereof.